1. Field of the Invention
The present invention relates to a method of forming a connecting conductor and wirings of a semiconductor chip. In particular, the present invention relates to a method of forming a connecting conductor connected to a connection pad and is suitable for a semiconductor chip mounted on a build-up multi-layer substrate, and to a method of forming wirings connected to the connecting conductor.
2. Description of the Related Art
Recent development of performance and miniaturization of IC chips require to increase a wiring density of a substrate on which an IC chip is mounted, and a number of pins provided to the substrate or the IC chip. A build-up multi-layer substrate can be given as an example of a present-day high density mounting substrate, which is practically used. An epoxy resin layer is formed on a glass epoxy substrate that serves as a core substrate, and holes are formed in the resin layer by laser processing or photoetching in the build-up multi-layer substrate. An conductive pattern or a via conductor is then formed on the epoxy resin layer by using a copper plating, and multiple layers are subsequently formed by repeating the same processes over and over, completing the build-up multi-layer substrate. The build-up multi-layer substrate is electrically connected to a semiconductor chip to form a semiconductor device. Such a semiconductor device that is described above is also disclosed in U.S. Pat. No. 5,111,278.
According to a technique disclosed in JP 2001-15650 A, for example, an insulating resin layer is formed on a semiconductor chip. Solder bumps can then be given a narrow pitch by processing holes in the insulating resin layer in which a conductive paste layer connecting pads of the build-up multi-layer substrate and pads of the semiconductor chip is formed.
In this manufacturing method, the holes are formed by irradiating a laser beam on the insulating resin layer on the connection pads, after sealing the semiconductor chip with the insulating resin. Such a laser processing, however, can cause damage in the semiconductor chip. Furthermore, the laser processing cannot contribute to making the semiconductor chip smaller, or to giving the connection pads on the semiconductor chip with a narrower pitch.
Further, JP 2001-15650 A also discloses a technique of forming a hole in an insulating resin layer by using chemical developing.
A strong etching material is usually used as a developer to etch an epoxy resin generally used as the insulating resin. It is, however, difficult to use a strong etching material because such a strong material causes damage in a semiconductor chip. It is therefore extremely difficult to form holes having a high aspect ratio in the processed hole. That is, it is extremely difficult to make holes having a numeric value found by dividing the hole depth by a diameter of the largest opening portion. Accordingly, the hole forming process by using a chemical development on an epoxy resin that is on a semiconductor chip cannot contribute to giving the connection pads on the semiconductor chip a more narrower pitch.
Furthermore, JP 11-233678 A discloses a method of forming a hole for connecting pads of a semiconductor chip and pads of a build-up multi-layer substrate. A photosensitive resin is formed on the semiconductor chip, and a conventional photofabrication technique is applied to the photosensitive resin, thus the holes being formed.
If a photosensitive resin is used in direct contact with the semiconductor chip, however, it is difficult to ensure reliability over a long term of use because the temperature of the semiconductor chip can reach 60° C. or more during use. When considering that there is a tendency of increase in the amount of heat that is generated per unit surface area of the semiconductor chip as the chip size is made smaller and the chip is given higher functionality, this manufacturing method cannot contribute to making the semiconductor chip smaller, and cannot contribute to giving the connection pads on the semiconductor chip a more narrower pitch.